In a typical laser printer the media transport system may compose five major areas: (1) Pickup; (2) Registration; (3) Imaging; (4) Fuser; and (5) Output. Each area uses one or more rollers to move the media through the area. The linear velocities of all the rollers in the gear train are designed to be the same so that media transport speeds are synchronized in all areas. However, because of manufacturing process, part tolerances, material differences and different wearing characteristics of the rollers and gear train, the linear velocities of the rollers vary to a certain extent. As a result, media deformation such as waves, crimp, curl, wrinkles, paper jams, and print quality can occur.
For example, if the output roller's linear velocity is slower than that of the fuser roller, the fuser roller will feed the output roller more media than the output roller can handle causing media to start backing up, buckling up and folding up at the exit area of the fuser. Because of the high temperature in the fuser, the media exiting from the fuser is still in plastic form. As a result, permanent waves or deformation are formed in the backed up, buckled up, or folded up portion of the media. This phenomenon is more pronounced as the length of the media increases from A size (11 inches long) to B size (17 inches long). Paper jams can also occur because of this phenomenon.
If the output roller's linear velocity is faster than the fuser roller, the output roller pulls more media than the fuser roller can feed. Under these circumstances, the media is stretched at the fuser exit area while it is still in plastic form. Again, media deformation occurs and print quality may also be affected; additionally, the media may also be torn.